r - Given a vector, return a list of all combinations up to size n

Question

I'm trying to write a function in R that, given a vector and a maximum size n, will return all the combinations of elements from that vector, up to size n.

E.g.:

multi_combn(LETTERS[1:3], 2)

Would yield:

[[1]]
[1] "A"

[[2]]
[1] "B"

[[3]]
[1] "C"

[[4]]
[1] "A" "B"

[[5]]
[1] "A" "C"

[[6]]
[1] "B" "C"

I've figured out an inelegant way to run combn for each size up to n, but I can't seem to combine the results into a single list. Any suggestions?

Answer 1

Try this:

multi_combn <- function(dat, n) {
    unlist(lapply(1:n, function(x) combn(dat, x, simplify=F)), recursive=F)
}

which returns

> multi_combn(LETTERS[1:3], 2)
[[1]]
[1] "A"

[[2]]
[1] "B"

[[3]]
[1] "C"

[[4]]
[1] "A" "B"

[[5]]
[1] "A" "C"

[[6]]
[1] "B" "C"